1. Field of Invention
This invention pertains to thermosetting plastic foams, including polyurethane, polyisocyanurate, urethane modified polyisocyanurate, and phenol-formaldehyde foams, and particularly to the production of such foams using novel blowing agents.
2. Prior Art and Other Considerations
Cellular organic plastic foams made either by polymerizing phenol-formaldehyde resin, or made with urethane linkages, or made with isocyanurate linkages, or a combination, are well known in the art. Generally, these foams have been made by catalyzing a mixture of phenolformaldehyde resins, or by the catalyzed reaction between polymeric multi-functional polyisocyanates and polyols, as well as the trimerization of the polymeric polyisocyanate, in the presence of commercially available, and low cost blowing agents to form the cellular structure and low density.
The value of a blowing agent lies, in some measure, in its ability to boil at a low enough temperature that closed cells are formed inside the liquid, or semi-liquid, thermosetting plastic prior to the plastic becoming too "solid" to allow the gas to expand. Thus, ethyl alcohol, which boils at 78.3 degrees Celsius is not a suitable blowing agent by itself, because most usable foams will become semi-solids by the time they reach that temperature. Likewise, a blowing agent must be miscible with the resin it is mixed with, so that the particles of blowing agent are well distributed throughout the resin.
The prior art is replete with references to the art of blowing thermosetting resins to form low density foam products. The predominate blowing agent used in commercial rigid foam products made from thermosetting plastics has been tricloromonofluoromethane (CFC-11), either alone or in conjunction with other blowing agents.
The recent advent of partially hydrogenated chlorofluorocarbons (called "HCFCs") as a blowing agent material presents both new problems and new opportunities, for the preparation of low density cellular foams.
The early work using the new HCFCs alone, or in conjunction with CO.sub.2 gas, has shown the rapid diffusion of both the HCFC gas and the CO.sub.2 gas out of the foam cells. The most preferred new HCFC is HCFC-141b, which shows a particular tendency to escape rapidly from the foam cells. The other new blowing agent for thermosetting foams is HCFC-123, which does not diffuse through prior art cell walls as rapidly as does HCFC-141b.
Another new class of blowing agents is non-chlorinated, partially hydrogenated fluorocarbons, having the general formula H.sub.x F.sub.y C.sub.z. Yet another similar class of blowing agents is partially hydrogenated fluorocarbon ethers with the general formula H.sub.x F.sub.y C.sub.z --O--C.sub.m F.sub.n H.sub.p. Both classes are referred to herein as "partially hydrogenated fluorocarbons" and abbreviated as "HFCs". Neither of these classes include chlorine. Yet another class of blowing agents is fully fluoronated fluorocarbans with the general formula F.sub.y C.sub.z. This class is abbreviated "FCs".
A new class of polyols has been described in the U.S. application Ser. No. 07/495,616, filed Mar. 19, 1990, incorporated herein by reference. This new class of polyols substantially reduces the rate of diffusion of the new HCFCs out of the urethane modified polyisocyanurate foam cells made with these polyols.
Accordingly, it is an object of the present invention to provide a thermosetting foam having a good thermal resistance value, and a method of producing the same using a novel blowing agent system which has a slow rate of diffusion out of the foam cells.
An advantage of the present invention is the provision of blowing agents that facilitate improved long-term R-values of plastic foams.
An advantage of the present invention is the provision of several alternative combinations of blowing agents, thereby offering the foam insulation designer multiple choices.
Another advantage of the present invention is the use of common materials with low costs to be used as blowing agents.
Yet another advantage is the provision of a blowing agent system which reduces or eliminates the use of CFC and HCFC gasses, thereby eliminating the potentially harmful effects of chlorine on the environment.